Access Control

This assignment is to write an access control list interpreter for
some multi-access system.  You can imagine that it's a web server or
a database; those details don't matter.

The input is a sequence of {ACL, commandseq}.  Each ACL is itself a
sequence of lines; each 'commandseq' is a sequence of zero or more
commands.  The input is thus structured like this:

	acl1 line1
	acl1 line2
	acl1 line3
	...
	acl1 lineN
	command1a
	command1b
	acl2 line1
	acl2 line2
	acl2 line3
	...
	acl2 lineN
	command2a
	command2b
	...
	aclM line1
	aclM line2
	aclM line3
	...
	aclM lineN
	commandM

The list of entries in an ACL may be arbitrarily long.

An ACL line looks like this:

	user group permissions

where 'user' and 'group' are sequences of letters or digits.  A 'permission'
is either '-', for no permissions, or some sequence of the letters 'r', 'w',
'c', and 'x'.  The three fields are separated by any amount of white space.
A user or group of '*' is a wildcard; it matches all users or groups.

A command starts with an '/' and looks like this:

	/user group operation

where 'user' and 'group' are as above and 'operation' is either 'r', 'w', 'c',
or 'x'.  When multiple commands follow a single ACL, they are all interpreted
with respect to the single, preceeding ACL.  Note: wild cards are not
permitted on commands, only in ACL entries.

Empty lines should be ignored; any text following a # is a comment and
should be ignored.  These requirements make it easier to structure and
understand the test data.

Access Control Lists are, as mentioned in class, order-sensitive.  Any
operation not explicitly permitted by an ACL is to be denied.

The output from the program should list each command, a failure message
if appropriate, and the ACL line that permitted it if it succeeded.